A. Technical Field
The present invention relates to attaching means for attaching a blade section of a fan blade, in particular of a smoke extractor fan, to a fan hub.
The invention also relates to a fan blade, in particular for smoke extractor fans, with attaching means for attaching the fan blade to a fan hub and with a blade section.
B. Background of the Invention
Fans for subways or tunnels and/or closed vehicle buildings, such as underground parking garages, for example, must operate reliably for extremely long service lives with a variety of load and ambient conditions. Typically, the installation of fans in subways, tunnels or underground parking garages is designed for an operation over several years or decades. In particular with the use of fans as a smoke extractor fan in subways or tunnels there are requirements on the part of the subway or tunnel operator for the operability of the fan at high temperatures, such as occur in particular in the case of fires. The requirements are in part stipulated by law.
On the other hand, as is generally customary, there is an effort to produce fans as cheaply as possible and as economically as possible in terms of materials. In general, fans are composed in terms of their basic structure of a fan hub, to which a number of generic fan blades are radially attached. The attachment of the generic fan blades is carried out with the aid of generic attaching means, which are usually embodied as blade bases.
Various fans are known against the background of the general requirements for fans described above. In order to keep the weight low, fans are known, the fan blades of which are cast solid of aluminum or an aluminum alloy. However, the disadvantage of fan blades made of aluminum is their limited usability at temperatures above approx. 300° C. The tensile strength of aluminum decreases considerably at the cited temperatures, so that the aluminum gradually begins to flow. Even special aluminum alloys, such as sand-casting alloy, cannot substantially improve this inadequacy. As a result of this disadvantageous property of aluminum, fan blades produced of cast aluminum can be detached from the hub at high temperatures, such as can occur in the event of fires.
Due to this inadequacy of fan blades made of aluminum, in the prior art for smoke extractor fans under high stresses, that is, at high speeds and/or with large blade lengths, fan blades cast solid from steel are used. However, fans with solid cast steel blades are disadvantageously very heavy.
From DE 10 2004 010 397 A1 a blade is known for the blade wheel of a fan, in which an inner support part composed of a tough, high-strength material is cast around by an outer part of aluminum or a comparable light metal alloy such that it is embedded therein. The inner support part in turn is composed of two plates, which are inserted into one another through slots formed in each plate such that they are at right angles to one another seen in the direction of sight of the blade axis. The known blade is connected to the hub in that it is clamped between two hub bodies by compression. To this end the two hub bodies must be present disadvantageously as cast parts or they must be embodied expensively as a welded construction. This is unfavorable in particular with the individual production of large fans or with small batches.